Aerial drone

ABSTRACT

The disclosure relates to an unmanned aerial vehicle, wherein the fuel cell provides a structural component of the vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 15/571,258 filed Nov. 1, 2017, which is a 371 National Stage ofInternational Patent Application No. PCT/GB2016/051254 filed Apr. 29,2016, which claims priority to Great Britain patent application no.1507534.4 filed May 1, 2015, and Great Britain patent application no.1519214.9 filed Oct. 30, 2015, the disclosure of all of which areincorporate by reference herein in their entirety.

The present invention relates to aerial vehicles and, in particular, tounmanned aerial vehicles.

Aerial vehicles, or aircraft, may be powered or unpowered. Unpoweredaircraft include gliders and some lighter-than-air vehicles, such asballoons. Powered aircraft generally include planes, helicopters orother rotorcraft, microlights, and other lighter-than-air vehicles, suchas airships.

Unmanned aerial vehicles (UAVs) have many applications includingreconnaissance, remote sensing and providing an airborne base for atelecommunications transceiver.

UAVs are typically smaller than manned aircraft and may weigh between afew grams and 20 kilograms, for example. The expression “unmanned aerialvehicle” as used herein is intended to encompass aerial vehicles notcapable of conveying a pilot.

UAVs typically require power in order to provide propulsion, which mayin some cases be necessary in order for a UAV to remain airborne for aprolonged period, and power for auxiliary functions such as image orvideo capture, signal telemetry, or other on-board systems. In addition,for many applications the computing power required on-board the vehiclein order to provide the necessary functionality may represent asignificant power demand. This is particularly the case in autonomousUAV applications in which an onboard computer may make decisionsregarding flight path and the deployment of auxiliary functions. Such anautonomous UAV is pilotless in a strict sense. Alternatively, a UAV maybe piloted remotely and so although the vehicle itself is unmanned, itis still under human control.

Some conventional UAVs use primary cells to provide power, although itis now more common to use secondary cells such as lithium-ion batteries.A problem with conventional UAVs is that the flight time may be limitedbecause of the relatively high power demands of the propulsion and otheron-board systems. In recent years, photovoltaic panels have beenprovided on UAVs in order to extend the flight range in comparison toUAVs that have only primary or secondary cells. However, the powergenerating capacity of a photovoltaic panel depends on the ambientweather condition and the time of day and so photovoltaic panels may notbe appropriate for use in all circumstances. In addition, the powergeneration capacity of photovoltaic panels may be inadequate for someapplications in which either high power (speed) propulsion is requiredor the on-board systems of the UAV that provide its functionality areparticularly heavy or demand substantial electrical power.

According to one aspect of the disclosure there is provided an unmannedaerial vehicle comprising a plurality of at least one type of fuel cellsystem component distributed about the vehicle.

The at least one type of fuel cell system component may be a fuel cell.The at least one type of fuel cell system component may comprise atleast one of: a fuel cell, a fuel generator; a coolant structure; a fuelreservoir; and a reactant reservoir.

Each reactant reservoir may comprise a removable cartridge. The fuelgenerator or reactant reservoir may comprise a catalyst for catalysing areaction to generate fuel for a fuel cell. The vehicle may be arotorcraft. The rotorcraft may comprise a body and a plurality ofpropulsion modules. Each propulsion module may be coupled to the body bya respective strut. The struts may comprise the fuel cell systemcomponents. Each strut may comprise one or more of the fuel cell systemcomponents. The vehicle may be of a modular construction. One or more ofthe struts may be detachable from the body.

One of, or a plurality of, the struts may comprise a reactant reservoiror fuel reservoir. One of, or a plurality of, the struts may comprise acoolant structure. One of, or a plurality of, the struts may comprise aplurality of different types of fuel cell system component. One of, or aplurality of, the struts may comprise a fuel cell and a fuel generator.A type of fuel cell component that generates more heat when in usecompared to another type of fuel cell system component may be providedcloser to the propulsion module than the other type of fuel cell systemcomponent.

The body may comprise a reactant or fuel reservoir and/or a fuel cell.The fuel cell may provide a structural component of the vehicle. Eachfuel cell may comprise a plurality of fuel cell plates. The plates areorientated to be substantially aligned with each other so that theplates are vertical in use. A vertical air flow path may be providedthrough the plates.

Each propulsion module is associated with a respective fuel cell. An airinlet of each of the fuel cells may be associated with a respectivepropulsion module. Each propulsion module may be configured to provideoxidant and/or coolant to the associated fuel cell.

Each propulsion module may be the only active source of oxidant and/orcoolant to the associated fuel cell. Each propulsion module may have apropeller or rotor. The fuel cell may be integral with a surface of thevehicle. The fuel cells may provide power for propulsion of the vehicle.The fuel cells may provide power for auxiliary or on-board functions ofthe vehicle.

The unmanned aerial vehicle may comprise a controller. The controllermay be configured to receive electrical power from the fuel cells. Thecontroller may be configured to distribute the electrical power to thepropulsion modules.

According to a further aspect of the disclosure there is provided anunmanned aerial vehicle (UAV) comprising a fuel cell, wherein an airinlet of the fuel cell is associated with a propulsion module, andwherein the propulsion module is configured to provide oxidant and/orcoolant to the fuel cell. The propulsion module may be the only activesource of oxidant and/or coolant to the fuel cell.

According to a further aspect of the disclosure there is provided anunmanned aerial vehicle (UAV) comprising a body and a plurality ofpropulsion modules connected to the body by respective struts, in whichone or more of the struts comprises a fuel cell system component.

According to a further aspect of the disclosure there is provided adetachable strut for an unmanned aerial vehicle (UAV), in which thestrut comprises one or more fuel cell system components. The UAV may bea rotorcraft. A propulsion module may be coupled to the strut.

According to a further aspect of the disclosure there is provided anunmanned aerial vehicle (UAV) comprising a fuel cell, wherein the fuelcell provides a structural component of the vehicle.

Any feature described with reference to one of the aspects may beprovided in combination with the features of another of the aspects.

The use of an electrochemical fuel cell as a power source for anunmanned aerial vehicle is particularly advantageous because fuel cellscan offer improved power/weight and 35 power/volume ratio performancecompared to some prior art power supplies. In addition, a fuel cell canprovide the level of power demanded in modern UAV applications. Byincorporating the fuel cell into a structural component of the UAV, therelative weight added by the fuel cell can be reduced because the fuelcell performs both its primary purpose of power generation and providesa structural support required by the vehicle. As such, the efficiencyand performance of the UAV can be improved compared to prior artsolutions.

The fuel cell may be a planar fuel cell. The fuel cell may comprise aplurality of fuel cell plates. The plates may be orientated to bealigned with, or transverse to, a mechanical load associated with use ofthe vehicle, such as a direction of thrust from a propulsion unit of thevehicle. The vehicle may comprise a plurality of fuel cells. The fuelcells may be provided as a fuel cell stack. The fuel cells may bedistributed about the vehicle. The vehicle may comprise a plurality ofpropulsion modules. Each propulsion module may be associated with one ofthe plurality of fuel cells. An air inlet of the, or each, fuel cell maybe associated with the, or a particular, propulsion module. The, oreach, propulsion module may be configured to provide oxidant and/orcoolant to the, or the associated fuel cell. The, or each, propulsionmodule may be the only active source of oxidant and/or coolant to the,or the associated, fuel cell. The, or each propulsion module may have apropeller or rotor. The fuel cell may be integral with a surface of thevehicle. The fuel cell may provide power for propulsion of the vehicleor for auxiliary or on-board functions of the vehicle.

According to a further aspect of the disclosure there is provided anunmanned aerial vehicle comprising a fuel cell, wherein an air inlet ofthe fuel cell is associated with a propulsion module, and wherein thepropulsion module is configured to provide oxidant and/or coolant to thefuel cell. The propulsion module may be the only active source ofoxidant and/or coolant to the fuel cell.

According to a further aspect of the disclosure there is provided anunmanned aerial vehicle comprising a plurality of fuel cells. The fuelcells may be distributed about the vehicle. The vehicle may comprise aplurality of propulsion modules. Each propulsion module may beassociated with a respective one of the plurality of fuel cells.

According to a further aspect of the disclosure there is provided anaerial vehicle comprising a fuel cell.

The vehicles according to the any aspects may comprise any of thefeatures described with regard to any other aspect or features otherwisedescribed herein.

Embodiments of the present invention will now be described by way ofexample and with reference to the accompanying drawings in which:

FIG. 1 illustrates a schematic view of a glider comprising fuel cells;

FIG. 2 illustrates a schematic view of a plane comprising fuel cells;

FIG. 3 illustrates a schematic view of another plane comprising fuelcells;

FIG. 4a illustrates a schematic view of a rotorcraft comprising aplurality of fuel cells;

FIG. 4b illustrates a schematic longitudinal cross section through astrut of the rotorcraft of FIG. 4a ;

FIG. 5a illustrates a rotorcraft comprising a plurality of fuel cellsand a plurality of fuel generators;

FIG. 5b illustrates a schematic longitudinal cross section through astrut of the rotorcraft of FIG. 5a in which a fuel generator, a reactantcartridge and a fuel cell are located within the strut;

FIG. 5c illustrates a schematic longitudinal cross section through astrut in which a fuel generator, a first reactant reservoir and a fuelcell are located within the strut and a second reactant reservoir islocated within the body;

FIG. 5d illustrates a schematic longitudinal cross section through astrut in which a fuel generator and a fuel cell are located within thestrut and first and second reactant reservoirs are located within thebody;

FIG. 5e illustrates a schematic longitudinal cross section through astrut comprising a fuel cell and a fuel reservoir;

FIG. 6a illustrates a rotorcraft comprising a plurality of coolantstructures; and FIG. 6b illustrates a schematic longitudinal crosssection through a strut of the rotorcraft of FIG. 6a .

Throughout the present specification, the descriptors relating torelative orientation and position, such as “horizontal”, “vertical”,“top”, “bottom” and “side”, are used in the sense of the orientation ofthe unmanned aerial vehicle as presented in the drawings. However, suchdescriptors are not intended to be in any way limiting to an intendeduse of the described or claimed invention. Corresponding series ofreference numerals are used in the figures in order to refer to similaror corresponding features between different figures.

Electrochemical fuel cells convert fuel and oxidant, generally both inthe form of gaseous streams, into electrical energy and a reactionproduct. A common type of electrochemical fuel cell for reactinghydrogen and oxygen comprises a polymeric ion transfer membrane, alsoknown as a proton exchange membrane (PEM), within a membrane-electrodeassembly (MEA), with fuel and air being passed over respective sides ofthe membrane.

Protons (i.e. hydrogen ions) are conducted through the membrane,balanced by electrons conducted through a circuit connecting the anodeand cathode of the fuel cell. To increase the available voltage, a stackcan be formed comprising a number of series-connected MEAs arranged withseparate anode and cathode fluid flow paths. Such a stack is typicallyin the form of a block comprising numerous individual fuel cell platesheld together by end plates at either end of the stack. In general, theexpression “fuel cell” is used herein to encompass either a single fuelcell or a plurality of individual fuel cells assembled in series to forma fuel cell stack.

FIG. 1 illustrates a glider, which is an example of an unpowered aerialvehicle 100. The vehicle 100 has a body 102, a pair of wings 104, 106and a tailplane 108 with an upright portion. Each of the wings 104, 106and upright portion of the tailplane 108 comprises a fuel cell 109, 111,113. The fuel cells 109, 111, 113 may be configured to provide power toon-board systems such as telecommunication systems.

The fuel cells 109, 111, 113 each provide a structural component of thevehicle 100 in that they are integrated with a structural component ofthe vehicle. A structural component may provide a function of thevehicle 100. In this example, the fuel cells 109, 111, 113 are formed asunitary components with the wings 104, 106 and tailplane 108. Externalsurfaces of end plates of each of the fuel cells 109, 111, 113 may beaerodynamically shaped in order to at least partially provide thefunctionality of the structure with which they are integrated. Byproviding the fuel cells as part of structural components, as opposed toproviding additional components within the body 102 of the vehicle 100or providing an additional layer such as a photovoltaic skin on top ofstructural components, the overall weight of the vehicle 100 may bereduced. In some examples, one or more of the fuel cells 109, 111, 113may be configured to bear a mechanical load of the vehicle 100.

Examples of mechanical loads include those associated with flight orlanding.

The fuel cells 109, 111, 113 each have an air inlet 110, 112, 114 inorder to draw in oxidant and/or coolant. Such an arrangement may beparticularly advantageous for air cooled, open cathode fuel cells. Fansmay be provided at the air inlets 110, 112, 114 in order to draw in theair. Alternatively, the air inlets 110, 112, 114 may be fan less(without fans) and rely on the motion of the vehicle 100 through the airwhen in flight to draw air into the forward facing fans. Each fuel cell109, 111, 113 also has an air outlet (not shown), which may be provideddownstream of the air inlet 110, 112, 114.

An advantage of distributing the plurality of separate fuel cells 109,111, 113 around the vehicle 100 is that, in the event of a failure of aparticular fuel cell 109 due to, for example, the impact of a foreignobject such as a bird with its inlet 110, the remaining fuel cells 111,113 located at distal parts of the vehicle 100 may continue to operateand provide power as normal. A controller may be provided in order tomanage power production by the fuel cells 109, 111, 113 in accordancewith the demands of the vehicle 100.

A separate fuel supply module may be provided to each of the fuel cells109, 111, 113.

Alternatively, a central fuel supply module may serve the fuel cells109, 111, 113.

FIG. 2 illustrates a plane, which is an example of a powered aerialvehicle 200. The vehicle 200 is generally similar to the vehicledescribed with reference to FIG. 1, and in addition comprises apropulsion module 215. The propulsion module 215 is configured to propelthe vehicle 200 during flight. It will be appreciated that a widevariety of types of propulsion module are available. In this example,the propulsion module 215 comprises a motor configured to drive apropeller 216. In use, the propeller rotates in order to propel air overthe aerodynamic surfaces of the vehicle in order to generate both thrustand lift.

The propulsion module and air inlets 210, 212, 214 of the fuel cells209, 211, 213 in this example are arranged on the wings 204, 206 andupright portion of the tailplane 208 such that air is propelled by thepropulsion module into the air inlets 210, 212, 214 in order to provideoxidant and/or coolant to the fuel cells 209, 211, 213.

The fuel cells 209, 211, 213 may provide power for propulsion of thevehicle in addition to power for other on-board systems, which in thecontext of a powered flight vehicle may be considered to provideauxiliary functions. The propulsion module 215 may be an electric motorpowered by the fuel cells 209, 211, 213.

FIG. 3 illustrates another vehicle 300. The vehicle 300 is similar tothat described with reference to FIG. 2 and includes a plurality ofpropulsion modules 318, 320.

A first propulsion module 318 is associated with an air inlet 310 of afirst fuel cell 309. A second propulsion module 320 is associated withan air inlet 312 of a second fuel cell 311.

The first and second propulsion modules 318, 320 are configured toprovide oxidant and/or coolant to the respective first and second fuelcells 309, 311.

Each air inlet 310, 312 may have an open face that is transverse to, orsubstantially normal to, a direction of thrust from the propulsionmodule 318, 320 with which it is associated.

The air inlets 310, 312 of the first and second fuel cells 309, 311 maybe fanless and rely solely on the propulsion modules 318, 320 to drawair into the first and second fuel cells 309, 311. That is, thepropulsion modules 318, 320 may be the only active source of oxidantand/or coolant for the first and second fuel cells 309, 311. Anadvantage of such an arrangement is that the additional spatial volume,weight and material cost associated with additional fans for drawing airinto the fuel cells 309, 311 may be eliminated.

The first fuel cell 309 may be configured to provide power to the firstpropulsion module 318. The second fuel cell 311 may be configured toprovide power to the second propulsion module 320. In this way, thepower supply for the first propulsion module 318 may be providedseparately from the power supply for the second propulsion module 320.

Alternatively, power from both the first and second fuel cells 309, 311may be provided to both the first and second propulsion modules 318,320. One or more controllers may be provided in order to controloperation of the fuel cells 309, 311 in accordance with the demands ofthe first and second propulsion modules 318, 320 and, optionally, inaccordance with the power demand of any other on-board systems on thevehicle 300.

As in the vehicle of FIG. 2, the vehicle 300 comprises a third fuel cell313 provided in the tailplane 308. An air inlet 314 of the third fuelcell 313 is independent of the airflow directly driven by the first andsecond propulsion modules 318, 320. A fan may be provided at the airinlets 314 in order to draw in air to the fuel cell 313. Alternatively,the air inlet 314 may be fanless and rely on air to be drawn into theforward facing air inlet 313 by the motion of the vehicle 300 throughthe air when in flight.

FIGS. 4 to 6 provide examples of unmanned aerial vehicles that comprisea fuel cell system with a plurality of at least one type of fuel cellsystem component. Each type of fuel cell system component is distributedabout the vehicle so that each component of a particular type isspatially separated from other components of that type.

FIGS. 4 to 6 each illustrate a quadcopter, which is an example of arotorcraft 400, 500, 600. Each rotorcraft 400, 500, 600 comprises a body438 and a plurality of propulsion modules 440-443. The body is locatedcentrally with respect to the plurality of modules and may also bereferred to as a central body 438. A controller and/or other on-boardsystems of the rotorcraft 400 may be provided within the central body438. The propulsion modules 440-443 are coupled to the central body 438by respective struts 444-447, which may also be referred to as arms, orlimbs, of the rotorcraft 400, 500, 600. The struts 444-447 are examplesof structural components of the rotorcraft 400, 500, 600. Eachpropulsion module 440-443 comprises a motor that is configured to drivea respective rotor 448-451. The rotors 448-451 provide thrust and liftfor the rotorcraft 400, 500, 600 in a conventional manner.

In FIG. 4a , the rotorcraft 400 comprises a plurality of fuel cells452-455 distributed about the vehicle. Each of the struts 444-447comprises a fuel cell 452-455 having an air inlet 456-459 on a topsurface of the strut, an air outlet (not shown) on a bottom surface ofthe strut and an air flow path within the struts 444-447 between therespective air inlets 456-459 and air outlets. The fuel cells 452-455comprise plates, such as bipolar plates, that are aligned verticallywithin the struts 444-447. Each fuel cell 452-455 may be provided by anindividual fuel cell or fuel cell stack.

In some examples, each fuel cell 452-455 may provide one of the struts444-447. That is, each fuel cell 452-455 may be integrally formed withone of the struts 444-447. Such fuel cells 452-455 are configured tobear a mechanical load placed on the struts 444-447 by the central body438 and the propulsion modules 440-443. Additional mechanical loadsinclude those associated with flight or landing. The plates of the fuelcells 452-455 are orientated to be aligned with mechanical loads, suchas the direction of thrust of the propulsion modules 440-443, when thevehicle is in use. The plates of the fuel cells 452-455 may beespecially rigid perpendicular to a plane of the plates and so resist aforce applied in the vertical direction by the propulsion modules440-443.

In FIG. 4a , each air inlet 456-459 is associated with a respectivepropulsion module 440-443 and each propulsion module 440-443 isconfigured to provide air as an oxidant and/or coolant to a respectivefuel cell 452-455.

As in the example described with reference to FIG. 3, the air inlets456-459 of the fuel cells 452-455 may be fanless and rely solely on thepropulsion modules 440-443 to draw air into the fuel cells 452-455. Thatis, the propulsion modules 440-443 may be the only active source of airto provide oxidant and/or coolant for the fuel cells 452-455.

The rotorcraft 400 may have a modular construction in which the struts444-447 are detachable from the central body 438 using a clip-onarrangement, for example. Such an arrangement may enable the body 438 tobe extensible in order to change the payload carrying capability of therotorcraft 400. An extended body may be able to accommodate a greaternumber of clip-on struts and so carry a greater weight. By providing afuel cell system component in the strut 444-447, the power generatingcapability of the rotorcraft 400 can be varied accordingly with thenumber of propulsion modules 440-443. In addition, the provision of amodular construction of the rotorcraft 400 may be useful in reducing avolume of space occupied by the rotorcraft 400 in storage.

FIG. 4b illustrates a schematic longitudinal cross section through oneof the struts 444 of the rotorcraft 400 of FIG. 4a . In this view, theair inlet 457 and the air outlet 470 are visible on respective faces ofthe strut 444. The air inlet 457 faces the rotor 448 in order to receivethe oxidant and/or coolant for the fuel cell 452. An air flow path 472is provided from the rotor 448 of the propulsion device 440 to the inlet457 of the fuel cell 452, through the fuel cell 452 within the strut 444and is exhausted from the outlet 470 on the reverse face of the strut444. The fuel cells 452-455 are orientated so that the air flow path 472through the fuel cells is aligned with a downdraught produced by thepropulsion modules 440 in order to reduce drag.

FIG. 5a illustrates a rotorcraft 500 comprising a plurality of fuelcells 552-555 and a plurality of fuel generators 560-563. The pluralityof fuel cells 552-555 and fuel generators 560-563 are each distributedabout the rotorcraft 500. Each of the struts 444-447 comprises one ofthe plurality of fuel cells 552-555 and one of the plurality of fuelgenerators 560-563. Each of the plurality of fuel cells 552-555 has aninlet 556-559. The arrangement of the fuel cells 552-555 and respectiveinlets 556-559 is generally similar to that described previously withreference to FIG. 4a .

The fuel generators 560-563 may be provided by known hydrogen generatorsthat are configured to react a first reactant, such as sodiumborohydride, with a second reactant, such as water, in order to generatefuel, such as hydrogen gas, for consumption by the fuel cells 552-555.The fuel generators 560-563 may comprise a catalyst for catalysing thereaction to generate hydrogen gas from the first and second reactants.Such reactions are typically exothermic.

The temperature that is reached in the fuel generators 560-563 duringuse may be lower than would be the case if the same volume of fuelgenerator was provided at a single, centralised location in therotorcraft 500, rather than distributed about the rotorcraft 500.

As such, the requirements for cooling of the fuel generators 560-563 maybe reduced. This is advantageous because cooling systems, such as fansand heat sinks, may add additional bulk and weight to the rotorcraft andso reduce its efficiency.

A fuel generator typically generates more heat that a fuel cell when inuse and so in this example the fuel generators 560-563 are providedcloser to the propulsion modules 440-443 than the fuel cells 552-555 inorder that the fuel generators 560-563 are subject to more cooling fromdowndraft from the rotors 448-451 of the propulsion modules 440-443.

Each fuel cell 552-555 may be associated with a respective propulsionmodule 440-443 such that each propulsion module 440-443 only receiveselectrical power from a particular fuel cell 552-555, which may be thefuel cell 552-555 provided in the strut 444-447 that is connected tothat particular propulsion module 440-443.

Each fuel generator 560-563 may be provided with a respective reactantreservoir for one or more reactants. In order to avoid uneven depletionof the reactant reservoirs associated with the fuel generator 560-563,it is advantageous to provide a controller that is configured to:distribute electrical power from the fuel cells 552-555 to thepropulsion modules 440-443 in accordance with the requirements of thepropulsion modules and a remaining reactant level in each of thereactant reservoirs; and additional or alternatively to redistribute theone or more reactants between the reactant reservoirs 560-563 duringflight in accordance with variations in the reactant levels of thereactant reservoirs 560-563. The redistribution of the one or morereactants may assist in maintaining an appropriate weight balance of theunmanned aerial vehicle and so ensure that its flight characteristicsremain within expected parameters. The redistribution of the one or morereactants may be achieved by transferring the one or more reactantsdirectly between the various reactant reservoirs 560-563. In some cases,the controller may be configured to adjust a flying mode of the unmannedaerial vehicle, such as its direction, in order to change the fuelconsumption from the various reactant reservoirs and so rebalance therelative distribution of the one or more reactants.

Various options for arranging fuel cell system components within one ofthe struts 444 and the body 438 are described below with reference toFIGS. 5b to 5e . Similar arrangements may be provided in the otherstruts 445-447 described with reference to FIG. 5a .

FIG. 5b illustrates a schematic longitudinal cross section through astrut 444 of the rotorcraft of FIG. 5a . In addition to the componentsdescribed with reference to FIG. 5a , the strut 444 has a bay forreceiving and interfacing with a removable reactant cartridge 573. Thebay for the removable reactant cartridge 573 is situated adjacent to thefuel generator 560 within the strut 444.

In this example, the reactant cartridge 573 provides a reservoir for atleast one reactant. The reactant cartridge 573 may comprise a firstreservoir for a first reactant and a second reservoir for a secondreactant. Alternatively, the reactant cartridge 573 may comprise asingle reservoir to store a mixture of the first and second reactantsand a reaction retarding chemical. A catalyst may be provided in thereaction chamber 560 in such examples to overcome the reaction retardingeffects of the chemical. Sodium hydroxide, for example, may be used as areaction retarding chemical in the case where the first reactant issodium borohydride and the second reactant is an aqueous solution suchas water. Other examples of first reactants for use with an aqueoussecond reactant include other metal borohydrides, nano-silicon,aluminium and other metals made active for water splitting, lithiumhydride, lithium aluminium hydride, sodium aluminium hydride, calciumhydride and sodium silicide. In other examples, a thermolysis fuel maybe used in the least one reactant. Thermolysis fuels include ammoniaborane, aluminium hydride (alane) and magnesium borohydride. There arealso fuels that require the use of a reformer, such as methane orbutane, for example.

Providing fuel cell system components such as the removable reactantcartridges within the struts 444-447, as opposed to elsewhere in thedrone, may reduce the drone surface area and volume because the strutswould otherwise provide unoccupied space.

A first air flow path 572 a and a second air flow path 572 b are alsoshown in FIG. 5b . The first air flow path passes through the fuel cell452 in a similar manner to that described with reference to FIG. 4b ,although in this case the position of the fuel cell 452 is furtheroffset from the propulsion module 444 along the length of the strut 444.The second air flow path 572 b flows around a portion of the strut 444that houses the fuel generator 560 and the reactant cartridge 573,rather than through the strut 444. Cooling is therefore provided to thefuel generator 560 and the reactant cartridge 573 through a surface ofthe strut 444.

The portion of the strut 444 that houses the fuel generator 560 and thereactant cartridge 573 may take a conventional aerodynamic design inorder to avoid disturbing airflow and creating drag.

FIG. 5c illustrates a schematic longitudinal cross section through analternative arrangement of the strut 444. A fuel cell is not shownwithin the strut 444 in order to enable the other fuel cell systemcomponents to be shown more clearly. A fuel cell may be provided withinthe strut 444 of FIG. 5c in a similar manner to that described withreference to FIG. 5b .

In this example, the reactant cartridge 573 provides a first reactantreservoir for a first reactant, such as sodium borohydride. A secondreactant reservoir for holding a second reactant, such as water, isprovided within the central body 438. In this case, the strut 444 has aconduit 576 for providing the second reactant from the second reactivereservoir 574 in central body 438 to the fuel generator 560 within thestrut 444. The second reactant reservoir 57 4 may be provided as acartridge or as a refillable container. The strut 444 also has anoptional conduit 578 for transporting reactant by-product from the fuelgenerators 560-563 to an optional waste storage portion 580 of thecentral body 438.

Typically, a reactant reservoir may be a relatively heavy component ofthe UAV when it is full of water. Providing heavy components closer tothe centre of mass of the UAV reduces the rotational inertia of the UAVand so improves its agility and manoeuvrability. Further, heating of thewater within the second reactant reservoir 574 may be avoided byproviding the second reactant reservoir 574 distally from the fuelgenerator 560.

As an alternative to the example shown in FIG. 5c , the reactantcartridge 573 may be omitted and the second reactant reservoir 574 maybe the only reactant reservoir for the fuel cell in the strut 444. Forexample, a mixture of a first reactant, a second reactant and a reactantretarding chemical may be provided within the second reactant reservoir574 as described previously.

FIG. 5d illustrates a schematic longitudinal cross section through afurther alternative arrangement of the strut 444. In this example, thefuel cell (not shown) and fuel generator 560 are provided within thestrut 444 as described previously with reference to FIGS. 5b and 5c .This example differs from that described with reference to FIG. 5c inthat the first reactant reservoir is provided within the central body438. In this example, the first reactant reservoir is provided as areactant cartridge 573.

FIG. 5e illustrates a schematic longitudinal cross section through afurther alternative arrangement of the strut 444 which differs from theexample described with reference to FIG. 5b in that the fuel generatoris omitted. The reactant cartridge of FIG. 5b is replaced by a removablefuel cartridge 586 within the strut 444. The removable fuel cartridgecontains fuel, such as hydrogen gas, for a fuel cell 585 within thestrut rather than precursor reactants for generating fuel for the fuelcell 585. Typically, the fuel cell 585 may generate more heat than thefuel cartridge 586 when in use and so the fuel cell is positioned closerto the downdraught from the rotor 448 than the fuel cartridge 586. Airflow from the rotor 448 flows over a surface of the fuel cartridge 586in a similar manner to that described previously for airflow over thefuel generator and reactant cartridge in previous examples.

The fuel cartridge 586 may be conventionally aerodynamically shaped inorder to avoid disturbing airflow and creating drag.

FIG. 6a illustrates a rotorcraft 600 comprising a fuel cell system witha plurality of coolant structures 646, 648. The coolant structures 646,648, which may be provided by heat pipes, act as heat sinks for othercomponents of the fuel cell system. The coolant structures 646, 648 areprovided within some of the struts 445, 447 in this example. The coolantstructures 646, 648 may provide structural components of the struts 445,447, that is, they may bear the load of the propulsion modules 441, 443and the loads inflicted upon the rotorcraft 600 during flight.

Each of the coolant structures 646, 648 is associated with a differentpropulsion module 441, 443, which acts as an active source of coolantair for the coolant structure 646, 648 so that the flow of air around orthrough the coolant structure cools the fuel cell components within thecentral body 438.

In this example, the central body 438 comprises fuel cell systemcomponents including a fuel cell (not shown in FIG. 6a ). The fuel cellsystem components within the central body 438 are thermally coupled tothe coolant structures 646, 648 in order for excess heat to be conductedaway from the fuel cell components and dissipated. An air inlet 650 forthe fuel cell is shown on a top surface of the body 438. The air inlet650 of the fuel cell is arranged to receive ambient air or disturbedairflow from the propulsion modules 441, 443.

FIG. 6b illustrates a schematic longitudinal cross section through oneof the struts 441 of the rotorcraft 600 of FIG. 6a . The body 438 has abottom surface comprising an air outlet 688 provided on a reversesurface to the top surface that comprises the air inlet 650.

A fuel cell 691 is provided within the central body 438. A first airflow path 692 is provided through the body 438 from the air inlet 650,through the fuel cell 691 and out of the air outlet 688. The airexhausted from the air outlet 688 contributes to a downdraught of therotorcraft 600.

A second air flow path 690 is provided by air disturbed by the rotor 449of the propulsion module 441. The second air flow path 690 passesthrough a portion of the strut 445 composed of the coolant structure646. The second air flow path 690 cools the coolant structure 646 byconvection and so dissipates heat. In this way, heat is drawn away fromthe fuel cell system components that are thermally coupled to thecoolant structure 646 and so the overall temperature of the fuel cellsystem components is reduced.

In an alternative example, one or more coolant structures within thestruts may be provided in an arrangement such as those described withreference to FIGS. 5a to 5e .

The following description of an unmanned aerial vehicle is alsodisclosed. The vehicle comprises:

(I) a fuel cell (FC) integrated with/near propeller module therebyproviding air flow to FC with the propeller and/or airspeed without needof additional fans—this also provide more redundancy to the airframe inthe event that some of it is not working.

There is, de facto, distributed power across the airframe so not allprop modules stop at the same time if one FC fails. The fuel may also bedistributed or centralised.

(II) FC as part of the structural struts and/or beam parts of theairframe itself (I) can be combined with (I) above if the FC is near thepropellers, e.g. with beams connecting the main body of a quadcopter orsuch to the propeller/electrical motor module. A fuel cell stack is madeof plates so is especially rigid in the plane perpendicular to thebipolar plates.

(III) a planar FC, with external and internal surfaces of the airframe(chassis, enclosure/any surfaces whether active of passive transformedinto a power source.

This can be used either for main propulsion services or for hotelloads/APUs.

Further embodiments are intentionally within the scope of theaccompanying claims.

1. An unmanned aerial vehicle comprising a plurality of fuel cells,wherein the fuel cells provide a structural component of the vehicle;wherein the fuel cells are distributed about the vehicle and, whereinthe vehicle comprises a plurality of propulsion modules and eachpropulsion module is associated with a respective one of the pluralityof fuel cells.
 2. An unmanned aerial vehicle comprising a plurality offuel cells, wherein the fuel cells provide a structural component of thevehicle; and wherein an air inlet of each fuel cell is associated with arespective propulsion module.
 3. The unmanned aerial vehicle of claim 1,wherein each propulsion module is configured to provide oxidant and/orcoolant to the associated fuel cell.
 4. The unmanned aerial vehicle ofclaim 3, wherein each propulsion module is the only active source ofoxidant and/or coolant to the associated fuel cell.
 5. The unmannedaerial vehicle of claim 3, wherein each propulsion module has apropeller or rotor.
 6. The unmanned aerial vehicle of claim 3, whereinat least one fuel cell is integral with a surface of the vehicle.
 7. Theunmanned aerial vehicle of claim 3, wherein each fuel cell providespower for propulsion of the vehicle.
 8. The unmanned aerial vehicle ofclaim 3, wherein at least one of the plurality of fuel cells providespower for auxiliary or on-board functions of the vehicle.
 9. Theunmanned aerial vehicle of claim 2, wherein each propulsion module isconfigured to provide oxidant and/or coolant to the associated fuelcell.
 10. The unmanned aerial vehicle of claim 9, wherein eachpropulsion module is the only active source of oxidant and/or coolant tothe associated fuel cell.
 11. The unmanned aerial vehicle of claim 9,wherein each propulsion module has a propeller or rotor.
 12. Theunmanned aerial vehicle of claim 9, wherein at least one fuel cell isintegral with a surface of the vehicle.
 13. The unmanned aerial vehicleof claim 9, wherein each fuel cell provides power for propulsion of thevehicle.
 14. The unmanned aerial vehicle of claim 9, wherein at leastone of the plurality of fuel cells provides power for auxiliary oron-board functions of the vehicle.